The present invention relates to methods and apparatus for applying a polymeric coating to a substrate.
Processes and apparatus for application of polymer coatings onto moving webs have long been used in the manufacture of: carpets, fabrics (such as waterproof fabrics), decals, flexible composites, and many other commercially important articles. Coating polymeric layers onto web-type substrates has long been an area of great technological interest. Common coating methods include: dip coating, rod coating, knife coating, blade coating, air knife coating, gravure coating, forward and reverse roll coating, slot and extrusion coating, slide coating and curtain coating. See Cohen, E. in xe2x80x9cModern Coating and Drying Technology,xe2x80x9d Chap. 1, VCH Publishers, ISBN 1-56081-097-1.
A brief review of a few patents for coating apparatus and processes is provided below.
Zemlin in U.S. Pat. No. 3,891,785, issued in 1975, discloses a solvent-free, two-part system for forming a polyurethane coating. In Zemlin""s process, a rapidly mixed composition is deposited on a moving fabric. The fabric carries the composition under a knife member that limits the amount of composition carried forward and spreads the composition as a layer on the surface. A rolling bank is created in front of the knife member. Shear-thinning is an important property of Zemlin""s reaction mixture. As deposited on the moving surface, shear is very low and viscosity of the mixture can reach high values. Shear increases in the rolling bank, and reaches a maximum during the knifing process.
Herzhoff et al. in U.S. Pat. No. 3,893,410 discloses a cascade coater having an inclined flow plane interrupted by a delivery gap for each coating liquid. The liquids flow down to form a coating meniscus and are coated onto an upwardly moving sheet. Similarly. Russell in U.S. Pat. No. 2,761,791 describes a process in which four separate coating compositions are pumped onto slide surfaces down which they flow by gravity to form separate layers that flow down toward a coating bead. The four layers are picked up by an upwardly moving web to form a four layer laminate on the web.
Sitler in U.S. Pat. No. 4,139,662 discloses a coating apparatus in which two compositions are combined in a mixing head and dispensed through a hose the hose is attached to a conventional reciprocating device that causes the opening of the hose to reciprocate between ends of a trough. The trough is positioned above and perpendicular to a sheet material that travels thereunder. A threaded rod is positioned within the trough and meters the fast-reacting saturant from the trough, through a slot and onto the moving web of sheet material.
Fast setting chemistry is advantageous for applying polymer coatings; however, a significant problem is polymer setting within the coating apparatus. Mutch in U.S. Pat. No. 3,832,427 discusses the need to design apparatus that can be conveniently opened for manual cleaning, such as brushing and scraping. In Mutch""s apparatus, at the end of an operation, the controls are operated to lift the applicator die clear of the table and a solvent and air purge are blown through the mixer and applicator die. Even after this procedure, Mutch remarks that the internal surface of the die passages still need manual cleaning after the die is opened.
Pipken in U.S. Pat. No. 4,345,543 discloses a method and apparatus for coating a moving web. In this method, coating material is fed from a conduit directly into a coating bank. A web passes by one side of the coating bank. Coating material is pulled down between the web surface and the surface of a smoothing film that is backed by a pliable membrane. The force generated by the pliable membrane controls the thickness of the coating.
From the patent and scientific literature, it is clear that there has been a continuing desire for new processes that are more effective, faster, and require fewer resources (i.e., is less expensive). The need for apparatus that is capable of handling fast-setting mixtures and is easy to clean, has long been recognized. Additionally, environmental concerns, such as the desire to reduce or eliminate solvents and avoid spray processes (which can result in airborne pollution), have been of increasing importance over the last 30 years.
In one aspect, the invention provides a coating apparatus, comprising: a dispersive surface; a receiving support having a surface opposed to the dispersive surface; at least one chemical dispenser disposed such that, during operation, the dispenser can dispense a polymer precursor composition onto the dispersive surface; and a bank disrupter disposed in an area between the dispersive surface and the receiving support. Preferably, the dispersive surface and the receiving support define a gap therebetween such that, during operation, the polymer precursor composition flows along the dispersive surface toward the gap. During operation, a coating bank that occupies an area between the dispersive surface and the receiving support is disrupted by the bank disrupter.
In another aspect, the invention provides a coating apparatus, comprising: a dispersive surface; a web having a first surface opposed to the dispersive surface; and at least one oscillating chemical dispenser disposed such that, during operation, the dispenser can dispense a polymer precursor composition onto the dispersive surface without dispensing directly onto the web or a coating bank. The dispersive surface and the web define a gap therebetween such that, during operation, the polymer precursor composition flows along the dispersive surface toward the gap.
In a further aspect, the invention provides a coating apparatus, comprising: a web that is disposed on rollers such that, during operation, the web is moved by rotation of the rollers; the web having an upper and a lower surface, and a width; a chemical dispenser that is disposed such that it is capable of dispensing a polymer precursor composition onto the upper surface of the web; a secondary surface disposed opposite a portion of the upper surface of the web, wherein the secondary surface and the upper surface of the web are spaced from each other; a closest approach of the secondary surface to the upper surface of the web that defines a gap; and a moveable bank disrupter probe disposed such that, during operation, the probe extends into the bank of polymer precursor composition and moves in a direction parallel to the width of the web. During operation, a bank of polymer precursor composition forms adjacent to the gap. That the disrupter xe2x80x9cmoves in a direction parallel to the width of the carrier sheet,xe2x80x9d does not limit the probe to moving exclusively in this direction, for example, the probe could move in a zig-zag or wave pattern. However, in a preferred embodiment, the probe moves in a straight line parallel to the sheet widthxe2x80x94this configuration can be simple to construct, reliable in operation, yet provide effective disruption of the coating bank.
In another aspect the invention provides a process of applying a polymer to a substrate. The process comprises: forming a bank of the polymer precursor composition, wherein a portion of the bank is in contact with a surface of the substrate; disrupting the bank of polymer precursor composition; and moving the substrate past the bank of polymer precursor composition.
The invention also provides a process of using a coating apparatus to apply a polymer to a substrate. The coating apparatus comprises: a dispersive surface; a receiving support having a surface opposed to the dispersive surface; and at least one chemical dispenser that is disposed such that, during operation, the dispenser can dispense a polymer precursor composition onto the dispersive surface. The dispersive surface and the receiving support define a gap therebetween such that, during operation, the polymer precursor composition flows along the dispersive surface toward the gap. Preferably, the gap is disposed such that, during operation, gravity will pull the polymer precursor composition down the slope of the dispersive surface and toward the gap. The process comprises: passing a polymer precursor composition through a coating apparatus, dispensing a polymer precursor composition downwardly from the chemical dispenser onto the dispersive surface; moving the web simultaneously with dispensing the polymer precursor composition; and subsequent to the dispensing, cleaning the chemical dispenser and dispersive surface by flushing downwardly through the dispenser a cleaning solution that removes residual polymer precursor composition from the dispenser and the dispersive surface.
The invention further provides a composition comprising a mixture of dialkoxyy and trialkoxy hydroxyalkylenecarbamoylalkylene-alkoxysilanes in which the molar ratio of dialkoxy to triethoxy hydroxvalkylenecarbamoylalkylene-alkoxysilane is in the range from about 1:3 to about 3:1; and articles made from this composition. It has been discovered that articles made from this composition exhibit surprisingly good laundering durability after aging.
Many disclosed embodiments can provide numerous advantages such as: the ability to function without the use of solvents or nonreactive diluents, economical and reliable processing, the ability to use fast-setting reactive chemistry without clumping, processing that can be discontinued and apparatus that can be cleaned without significant downtime, the ability to rapidly change chemical components to vary product properties even during the same production run, the ability to operate with a single wide-bore dispenser, high production rates, the capability to operate at high web speeds over wide substrates, compatibility with a large variety of substrates, the ability to produce smooth polymer coatings without ribbing, gels or streaks, and/or final products that can exhibit desirable properties such as excellent adhesion and launderability.
These and other advantages are more fully shop n and described in the drawings and detailed description of this invention, where like reference numerals are used to represent similar parts. It is to be understood, however, that the drawings and description are for the purposes of illustration only and should not be read in a manner that would unduly limit the slope of this invention.
xe2x80x9cBank disrupterxe2x80x9d can be a static disrupter that disrupts rotational flow within a coating bank, or, more preferably, an active disrupter such as a moving probe. Although the active disrupter typically disrupts flow within a coating bank, flow analysis is not a requirement for defining the active disrupter.
xe2x80x9cCoating bankxe2x80x9d is a bank of polymer precursor composition that contacts the web and the dispersive surface and has a thickness greater than the thickness of the coating on the coated web.
xe2x80x9cDispersive surfacexe2x80x9d means any surface over which the polymer coating composition can flow.
A xe2x80x9ccarrier supportxe2x80x9d is a support for a web material.
A xe2x80x9cgapxe2x80x9d is the space between a knife member and the receiving surface (such as a web surface) that controls the thickness of the coating. In many, embodiments, the distance of this space varies and in this (most typical) case, the gap is defined by the closest approach of the knife member and the receiving surface. In many preferred embodiments, the dispersive surface is also the knife member.
xe2x80x9cMoveable substratexe2x80x9d means a web or other material capable of being moved through a coating bank.
xe2x80x9cPolymerxe2x80x9d means a molecule that is made up of at least five repeating units that are regularly or irregularly arranged.
xe2x80x9cPolymericxe2x80x9d means containing a polymer.
xe2x80x9cPolymer precursor compositionxe2x80x9d refers to a composition that comprises reactive monomers, oligomers, and/or polymers that, during processing, react to form higher molecular weight polymeric material.
A xe2x80x9creceiving supportxe2x80x9d is either a carrier support or a moveable substrate.